Many musicians when playing solo before an audience are aware of moments when their particular instruments, no matter how well played, fail to produce the fullness and variety of sounds needed during a performance. As a result, it has become popular for a solo musician to accompany himself by using a rhythm box or other chord generating device. An electronic organ is particularly well suited to provide the required accompaniment but the rather complex keyboard and pedal system of such an instrument normally demands the full attention of another musician and hitherto it has not been possible for a solo musician playing his own instrument to make use of even the chords of an organ. Consequently, there is need for a relatively simple and easily operated control unit which will serve such a purpose.